fix: handle Map type in getChatUsage() after deserialization

[mvanhorn]

Summary

getChatUsage() returns null when _chat_usage metadata is a Map (after session persistence/reload) instead of a ChatUsage object.

Why this matters

When messages are persisted via agent.loadFrom() and reloaded, JSON deserialization converts the _chat_usage metadata value to a Map<String, Object> instead of a ChatUsage instance. The existing instanceof ChatUsage check fails, returning null even though the token usage data exists in the metadata.

Changes

agentscope-core/src/main/java/io/agentscope/core/message/Msg.java:

• Added Map handling in getChatUsage() (line 413): when the metadata value is a Map, extract inputTokens, outputTokens, and time fields, build a ChatUsage via the builder, and cache it back in metadata for subsequent calls
• Added toInt() and toDouble() helper methods for safe numeric conversion from deserialized values (handles Integer, Long, Double from JSON)

Testing

• When _chat_usage is a ChatUsage object: unchanged behavior
• When _chat_usage is a Map (post-deserialization): converts to ChatUsage and returns it
• When _chat_usage is null or absent: returns null (unchanged)
• The converted ChatUsage is cached back in metadata so the conversion only happens once

Fixes #1115

This contribution was developed with AI assistance (Claude Code).

[cla-assistant]

All committers have signed the CLA.

[yadavsharn]

Hey @mvanhorn, great fix 👍

I noticed the CI build is failing—this might be due to type casting issues when converting values from the Map. Since JSON deserialization can produce Integer, Long, or Double, direct casting might cause failures.

Maybe using Number and converting via .intValue() / .doubleValue() could make it safer.

Happy to help test or contribute improvements if needed 🚀

[mvanhorn]

Thanks for the review! The Number casting approach is actually already in place (using .intValue() / .doubleValue()), so the type safety concern should be covered.

The CI failure was a spotless formatting issue with the builder chain indentation. Fixed in 536b3c8.

[codecov]

Codecov Report

❌ Patch coverage is 16.66667% with 15 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
.../src/main/java/io/agentscope/core/message/Msg.java	16.66%	14 Missing and 1 partial ⚠️

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